Does every beekeeper become a Queen Breeder?
No, depends on temperament and how many colonies you want or wish to offer for sale.
Of 15 cells from a grumpy queen - possibly, even likely, all of them would have gone!
why not take a frame of brood and eggs
Because the queen produced that way may be inferior to alternative methods where there are more than sufficient bees to nurse the brood and she will be produced in an 'emergency' situation, not as a supercedure impulse.
Home-bred queens like that may have unwanted temperament issues (and others) and a later choice/selection of offspring, to go forward as the gene pool, is a much better way to go. That is not so easy with just one or two colonies, if one also expects, or wants, a decent honey crop.
Regards, RAB